Detection system

ABSTRACT

An optical system having a light source means and a detector means for detecting one or more articles which by means of a conveyor move or are temporarily stationary under the means, where said article(s) has/have at least one reflective portion, and where light is emitted towards the article(s) from the light source means and reflected back towards the detector means. The optical system is characterised in that at a distance above the conveyor there is provided a lens, that the light source means and the detector means are located in or essentially in the same plane which is parallel to the plane of the lens and coincident with the focal plane of the lens, and that the optical axis of the lens is coincident with an axis perpendicular to the focal plane and located halfway between the light source means and the detector means.  
     The present invention relates to an optical system having a light source means and a detector means for detecting one or more articles which by means of a conveyor move or are temporarily stationary underneath the means, where said article(s) has/have at least one reflective portion, and where light is emitted towards the article(s) from the light source means and is reflected back towards the detector means.  
     In particular when detecting articles such as bottles in bottle crates, it is often difficult to obtain an unambiguous definition of each individual bottle in the crate, its size and type. This is due to the fact that such bottles must normally be viewed from above down towards the crate, and often whilst the crate is in motion.

[0001] The present invention is based on the use of an optical systemwherein specular reflections from all the bottles in a bottle crate willbe visible to a camera when the light source is defined and ispreferably point shaped. By having several pairs each consisting of acamera and a light source, the present optical system will be able toprovide depth of view by using disparity measurements, whereby it willbe possible to measure, for example, the height of the bottles and alsoof the crate.

[0002] According to the invention, the optical system is characterisedin that at a distance above the conveyor there is provided a lens, e.g.,a Fresnel lens, that is common to the light source means and thedetector means, that the light source means and the detector means arelocated in or essentially in the same plane which is parallel to theplane of the lens and coincident with the focal plane of the lens, andthat the optical axis of the lens is coincident with an axisperpendicular to the focal plane and lying halfway between the lightsource means and the detector means. This and additional embodiments ofthe optical system will apparent from the attached patent claims andfrom the following description with reference to the attached drawings.

[0003]FIG. 1 is a drawing showing the principle of the optical systemaccording to the invention.

[0004]FIG. 2 shows by way of example two light source/camera pairs.

[0005]FIG. 3 shows a variant of the combination of light source andcamera

[0006]FIG. 4 shows a further variant of two pairs each consisting of alight source and a camera

[0007]FIG. 5 shows an optical system consisting of two cameras and twolight sources in cooperation with one lens.

[0008]FIG. 6 shows a variant with a lens, and one camera and one lightsource.

[0009]FIG. 7 shows a solution for viewing the side portion of a case.

[0010]FIG. 8 is a simplified block diagram of function blocks that areincorporated in the optical system according to the invention.

[0011]FIG. 9 shows a variant with regard to the location of the lightsource and camera.

[0012] Basically, the system consists of a lens 1, for example, aFresnel lens, and where a reflective face 2 which is perpendicular tothe axis 3 of the lens 1 is formed by the reflective top 2 of a bottle4. The reflective top 2 of the bottle is on one side of the lens 1 andthe focal plane 5 of the lens is on the other side of the lens 1. Whenlight is emitted from a location 6 or 7 in the focal plane, it will bymeans of the specular effect from the reflective top of the bottle befocused on another point in the focal plane, just as far off the lensaxis 3, but on the opposite side thereof, and where a respective camera8 and 9 is located. Thus, the top of the bottle will be imaged inrespective camera 8 or 9. No other specular, direct reflection will beable to hit the camera. Height measurement can be done in many ways, forexample, by comparing images taken from different points in the focalplane and looking at the disparity of the top of the bottle in thedifferent images, thereby easily allowing an analysis of the bottleheight to be made on the basis of standard criteria which have beenentered in the system. The light source means will normally consist of nlight sources and the detector means will likewise consist of n cameras,where n >1. When n >2, all the pairs, each consisting of one lightsource and one camera, will be in the same focal plane of lens 1, likethe light source 6 and the camera 8, and the light source 7 and thecamera 9, and it will be seen in particular from FIG. 1 that a pointhalfway between the light source and the camera in each pair is on theoptical axis 3 of the lens.

[0013] In the illustrated example in FIG. 1 and also in FIG. 4, thelight source is preferably a point shaped light source. However, it isconceivable, as shown in FIG. 2, that the light source, indicated by thereference numerals 10 and 11 in this figure for respective lightsource/camera pairs 10, 12 and 11, 13, consists of a plurality of lightpoints 10′ and 11′ respectively. When the light source 10 and thus thecamera 12 are active, it is possible that some, but not all of the lightpoints 10′ are activated, or at least some of the light points 10′ areadapted to emit light that is coloured or to emit light of differentcolours and/or light intensity. The same can be provided for the lightpoints 11′ when the light source 11 and the detector in the form. of thecamera 13 are activated.

[0014] In FIG. 3 it is shown that the light source, in this caseconsisting of a plurality of light points 14, can surround a camera lens15 in a unit 16. Optionally, the light source may consist of an annularbody, or the annular body may in fact be formed of a plurality of lightpoints 14. The light points 14 will be related to a camera lens that islocated on a unit corresponding to unit 16, but diagonally relative tothe optical axis of the lens. Similarly, the lens 15 will be related toa light source, for example, in the form of light points 14 on thesecond (non-illustrated) unit which corresponds to the unit 16.

[0015]FIG. 4 shows a solution similar to that shown in FIG. 1 in moredetail and therefore the same reference numerals are used as in FIG. 1.

[0016]FIG. 5 shows an array of two light source/camera pairs, like thepairs 6, 8 and 7, 9 shown in FIG. 1 and FIG. 4 or the pairs 10, 12 and11, 13 in FIG. 2 or a solution as shown in FIG. 3 where the light sourcesurrounds a lens of a camera, the light source in the first of the pairssurrounding the camera lens in a second pair, and the light source inthe second pair surrounding the camera lens in the first pair. As willbe seen in FIG. 5, the two light source/camera pairs, as indicated bythe reference numerals 17, 18 are behind the same lens 19, in the focalplane of the lens 19, but on their respective sides of the optical axisof the lens. The height of articles, such as bottles in a case, iscalculated as is done traditionally in a stereoview system. Suchstereoview systems are generally known from a number of publications.

[0017] All light coming from a light source and hitting a horizontalreflecting face, such as a reflective top of a bottle, will hit theaperture of the camera located on the opposite side of the optical axis.As shown in FIG. 5, both long sides of a bottle case will be imaged andallow the possibility of logo recognition by using a separate lightsource to improve the illumination, as shown in more detail in FIG. 7,for example, by using a supplementary light source 20. However, it isalso conceivable that at a point laterally displaced from and along themovement path of the case, there is provided an alternative light source21 and/or an inclined mirror body 23 viewable by a camera (as forinstance, the camera 22), so that via said mirror body there is thepossibility of viewing a side portion 24 of a bottle crate 25 moreclearly. It is also possible that a light source 26, such as that shownin dotted lines, can be located on the upper side of the lens 27 andmade to emit light towards a partially transparent reflective face 28 soas to better illuminate the sides of the crate 25.

[0018] The variant shown in FIG. 6 is based on a light source and acamera behind the same lens, indicated in the figure by the referencenumeral 29. The light source is indicated in the figure by the referencenumeral 30, and the camera is indicated by the reference numeral 31. Aslit (not shown) which is rotated in front of the light source,preferably a point source, will provide a moving light plane at aconstant angle. All light that hits a horizontal, reflective face, suchas a reflective face on the top of a bottle, will be able to hit thecamera aperture of the camera 31. Depth of view can then be produced by15 triangulation given that the position of the light plane is known atthe time of imaging. The system is oriented so that the light plane scantakes place perpendicular to the conveyor direction in order to obtain aminimum scanning field and the possibility of logo recognition on thebottle crate 25.

[0019] In certain instances, as indicated in FIG. 9, it may be expedientto use an inclined, partially transparent mirror 35 in the light pathfrom a light source means 33, and where the detector means, indicated bythe reference numeral 32 in the figure, receives reflected light from anarticle via said mirror 35. The detector 32 and the light source 33 willbe at different physical distances from the lens 34, but nevertheless atthe same optical distance from the lens 34 and thus in respective focalplanes 36, 36′.

[0020] As indicated in the drawings, the respective light source andcamera in each pair have approximately equal aperture angles. In mostcases this is essential in order to obtain optimal measurement data.Although the lens, such as the lens 1, 19, 29 and 34 may be a Fresnellens, other types of lenses may also be used. However, it will bedesirable that the lens is provided with an antireflection coating,schematically indicated in FIG. 9 by the reference numeral 37. However,it will be appreciated that this antireflection coating, which is toprevent the lens itself from being perceived as the reflective face,will be extremely thin.

[0021] In FIG. 8, by way of example, two light source/camera pairs areindicated by the reference numerals 38, 39 and 40, 41. The units 38, 39are located diagonally relative to the optical axis 3 of the lens andthe same applies in the case of the units 40, 41. Optionally, asindicated in connection with, for example, FIG. 2, the light source 39can be split into a first light source member 39′ and a second lightsource member 39″. The same may be the case for the light source 41 withlight source members 41′ and 41″. If there is a need for any more lightsources, as for instance one or more of the light sources 20, 21 or 26,as shown in FIG. 7, such a light source is indicated in FIG. 8 by thereference numeral 42. The light sources and the cameras can becontrolled from a microprocessor 43. A camera image analyser (CIA) 44 isconnected to the microprocessor 43. A data bank 45 is provided in whichcertain standard image definitions are stored. A comparator 46 comparesthe output from the units 44 and 45 and outputs these to an output unit47 which gives a definition of the article or articles that are detectedby the optical system.

[0022] Further modifications of the optical system as taught within thescope of the attached patent claims are of course possible within thescope of the invention. The preceding illustrative exemplary embodimentsof the invention are merely to be seen as examples, and should not beunderstood as in any way restricting the scope of the invention.

1. An optical system having a light source means and a detector meansfor detecting one or more articles which by means of a conveyor move orare temporarily stationary under the means, where said article(s)has/have at least one reflective portion, and where light is emittedtowards the article(s) from the light source means and reflected backtowards the detector means, characterised in that at a distance abovethe conveyor there is provided a lens that is common to the light sourcemeans and the detector means; that the light source means and thedetector means are located in or essentially in a same plane which isparallel to the lens plane and coincident with a focal plane of thelens; that the light source means consists of n light sources; and thedetector means consists of n cameras,where na, 2; that all pairs eachconsisting of one light source and one camera, are in the same focalplane; that a point halfway between the light source and the camera ineach pair is on the optical axis of the lens, and that the optical axisof the lens is coincident with an axis perpendicular to the focal planeand is located halfway between the light source means and the detectormeans
 2. An optical system according to claim 1, characterised in thatthe light source is a point source.
 3. An optical system according toclaims 1 or 2, characterised in that the light source surrounds a lenson a camera, the light source in a first of the pairs surrounding thecamera lens in a second pair, and the light source in the second pairsurrounding the camera lens in the first pair
 4. An optical systemaccording to claim 3 characterised in that the light source is anannular body.
 5. An optical system according to claim 3, characterisedin that the light source consists of a plurality of light points, forexample formed of light emitting diodes or light guides.
 6. An opticalsystem according to one or more of the preceding claims, characterisedin that an inclined, partially transparent mirror is disposed in thelight path from said light source means; and that the detector meansreceives reflected light from the article via said mirror.
 7. An opticalsystem according to one or more of the preceding claims, characterisedin that the pairs consisting of a light source and a camera areactivated successively by a mutual time separation
 8. An optical systemaccording to one or more of the preceding claims, characterised in thatthe light source and the camera in each pair have approximately equalaperture angles.
 9. An optical system according to one or more of thepreceding claims, characterised in that the lens is provided with anantireflection coating.
 10. An optical system according to claim 1 or 9,characterised in that the lens is a Fresnel lens.
 11. An optical systemaccording to claim 5, characterised in that said light points areselectively activatable.
 12. An optical system according to clam 5 or11, characterised in that said light points emit coloured light; andthat at least some of the light points are arranged to emit light ofdifferent colours and/or light intensity.
 13. An optical systemaccording to one or more of the preceding claims, characterised in thatat a point laterally displaced from and along the movement path of thearticle there is provided a light source and/or an inclined mirror bodythat is viewable by a camera for viewing a side portion of the articlesor a crate in which the articles are placed.
 14. An optical systemaccording to one or more of the preceding claims, characterised in thatsaid articles are bottles placed in a bottle crate.